The present invention relates generally to utilizing controlled transmissions of electromagnetic (EM) energy through or across materials that have previously been barriers to their penetration to determine the thickness and EM characteristics of ferromagnetic materials.
It has long been possible to measure metallic thickness variations by electromagnetics. Prior methods have typically excited the metal by eddy currents or D.C. fields. After excitation, the known methods looked for variations in amplitude of the signal corresponding to variations in metallic thickness.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims.
To achieve the foregoing objects, features, and advantages and in accordance with the purpose of the invention as embodied and broadly described herein, a method is provided for creating a spectral EM frequency to calculate the thickness of a material with unknown permeability and conductivity using metallic transparencies. The method comprises the steps of (a) testing empirically to approximate the conductivity, (b) testing empirically to approximate the permeability, (c) creating a first set of electromagnetic waves adjacent to the material to be measured of a relatively low frequency, (d) impinging the first set of electromagnetic waves on the material for saturating the material, (e) creating a second set of electromagnetic waves having specific constant amplitude of a higher frequency than the first set of electromagnetic waves, the second set of electromagnetic waves for engaging the material and generating a sensing signal having modified characteristics, and (f) receiving the sensing signal through the saturated material such that the modified characteristics of the sensing signal are processed to determine the thickness of the material.
In another embodiment, a method for creating a spectral EM frequency to calculate the thickness of a material having a constant length L and varying frequencies with unknown permeability and conductivity is provided. The method comprising the steps of (a) calculating the penetration depth xcex4 using       δ    =                  (                  1          e                )            ⁢      L        and      δ    =          1                        σ          ⁢                      xe2x80x83                    ⁢                      μ            r                    ⁢                      μ            o                    ⁢          f                    
where
xcex4=penetration depth,
ƒ=frequency,
xcexcr=relative permeability, and
xcexco=absolute permeability,
(b) determining the relationship of frequencies such that
ƒ6 greater than ƒ5 greater than ƒ4 greater than ƒ3 greater than ƒ2 greater than ƒ1, and
(c) using the frequencies to determine the thickness of the material.